Field of the Invention
The present invention relates to a magnetoresistance effect element.
Description of Related Art
A giant magnetoresistance (GMR) element which is formed of a multilayer film including ferromagnetic layers and non-magnetic layers, and a tunnel magnetoresistance effect (TMR) element in which an insulating layer (a tunnel barrier layer or a barrier layer) is used as a non-magnetic layer are known. In general, a TMR element has a higher element resistance than a GMR element but has a higher magnetoresistance (MR) ratio than a GMR element. Therefore, a TMR element has attracted attention as an element for a magnetic sensor, a high-frequency component, a magnetic read head, or a magnetoresistive random access memory (MRAM).
A TMR element can be classified into two types depending on the mechanism of tunnel transport of electrons. In one type of a TMR element, only the penetrating effect (tunneling effect) of wave functions between ferromagnetic layers is used. In the other type of a TMR element, coherent tunneling (only electrons having a specific wave function symmetry tunnel), which is tunneling using a specific orbital transport of non-magnetic insulating layers, is predominant. It is known that, in a TMR element where coherent tunneling is predominant, a MR ratio higher than that of a TMR element in which only the tunneling effect is used is obtained.
In order to cause the coherent tunneling effect to occur, it is necessary that two ferromagnetic metal layers and a tunnel barrier layer be crystalline and that interfaces between the two ferromagnetic metal layers and the tunnel barrier layer be crystallographically continuous.
As a tunnel barrier layer in which the coherent tunneling effect can be obtained, a MgO layer is known. In addition, United States Patent Applications, Publication No. 2008/0138660 and Japanese Unexamined Patent Application, First Publication No. 2012-204348 describe that the coherent tunneling effect can be obtained in (MgZn)O in which Mg ions in MgO are partially substituted with Zn ions.
In addition, Japanese Patent No. 5586028 reports MgAl2O4 having a spinel structure as an alternative material to MgO. Japanese Unexamined Patent Application, First Publication No. 2013-175615 describes that MgAl2O4 having a disordered spinel structure is used as a tunnel barrier layer.